Science & Environment

How octopuses co-ordinate their arms

Octopus (c) Science Photo Library Image copyright SPL
Image caption The study is the first to examine how octopuses co-ordinate their eight, flexible limbs as they crawl

With the aid of high-speed cameras, scientists have revealed how octopuses co-ordinate their arms to crawl.

Researchers from the Hebrew University of Jerusalem filmed crawling octopuses to work out exactly how the animals used their almost limitlessly flexible arms when they move.

This revealed the surprising simplicity of their motion; they just choose which arm to use to push themselves along.

The findings are published in the journal Current Biology.

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Media captionPush-pull: The footage, captured by Dr Guy Levy, reveals how each arm moves the animal in a particular direction

The study is the first detailed analysis of exactly how octopuses manages to move without a rigid skeleton.

How octopuses control and move their soft bodies is of interest to engineers who aim to design biologically inspired robots.

"People want to build soft robots for medical purposes and rescue operations," said Dr Guy Levy, one of the researchers involved in the project.

Such soft-bodied, octopus-inspired arms would not be limited by fixed joints, he explained. This could be useful to access narrow, difficult to reach spaces - perhaps getting help to people trapped at the scene of a collapsed building.

Pick a leg

To find out the secrets of the octopus's remarkably efficient movement, Dr Levy and his colleague Prof Benny Hochner videoed the animals from underneath as they crawled, and analysed their motion frame by frame.

This detailed study showed that, by shortening and lengthening, each arm pushed the body in only one direction.

"So the octopus only has to decide which arm to use for the pushing - it doesn't need to decide which direction this arm will push," explained Dr Levy.

"[It has] found a very simple solution to a potentially complicated problem - it just has to pick which arm to recruit."

And because the creatures are able to push off any of their eight legs, they are able to crawl in any direction - no matter which way their body is facing. And, uniquely, there is no rhythm or pattern to their undulating limb movements

The scientists' next step is to delve into the internal circuitry of the octopus nervous system, to find out exactly how this co-ordinated crawling is controlled.

Dr Levy added: "Every time we try to understand something new about the octopus, there are new surprises."

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